WASHINGTON – A previously secret Justice Department memo, released by a federal appeals court Monday, justified the targeted killing of Anwar al-Awlaki, an American citizen who was killed by a drone strike in Yemen in 2011, on the grounds that as a leader of an al-Qaida affiliate, he was actively “engaged in hostilities against the United States.”

The 2010 memo was written by David Barron, the acting head of the Justice Department’s Office of Legal Counsel at the time, and concluded that neither the Constitution nor several federal statutes would prevent the president from ordering the killing of someone in al-Awlaki’s circumstances.

“At least where, as here, the target’s activities pose a ‘continued and imminent threat of violence or death’ to U.S. persons, ‘the highest officers in the Intelligence Community have reviewed the factual basis’ for the lethal operation, and a capture operation would be infeasible,” the killing would be considered a lawful act of war, the memo concluded.

The existence of the memo and the outline of its legal argument for why the government had authority to kill al-Awlaki, who was born in New Mexico, has been known for some time. But the release of a redacted copy by a federal appeals court in New York provided the first public view of the specifics.

The Obama administration had resisted efforts to release the document to the public, but lost that fight in the appeals court and decided against appealing further.

Barron, who wrote at least three memos on the subject, was recently confirmed as a federal judge after the Obama administration agreed to a demand from several senators that they be allowed to read the documents.

“In the present circumstances, as we understand the facts, the U.S. citizen in question has gone overseas and become part of the forces of an enemy with which the United States is engaged in an armed conflict; that person is engaged in continual planning and direction of attacks upon U.S. persons from one of the enemy’s overseas bases of operations; the U.S. government does not know precisely when such attacks will occur; and a capture operation would be infeasible,” Barron wrote.

In those circumstances, “the Constitution would not require the government to provide further process” such as advance notice or a court hearing before carrying out a deadly strike, he wrote.

In a statement, a lawyer representing al-Awlaki’s family criticized the legal reasoning in the memo.

“The DOJ memo confirms that the government’s drone killing program is built on gross distortions of law,” said Pardiss Kebriaei of the New York-based Center for Constitutional Rights.